(lt.39)Mastering Regular Expressions and Efficient Use of Spread & Rest Operators in JavaScript

A regular expression (regex) in JavaScript is a pattern used to match character combinations in strings. They consist of a sequence of characters and special metacharacters that define the criteria for the search.

// let pattern = "hello"
// //converted to regular expression
// // let regx = new RegExp(pattern)   // this conversion is optional

// let flag = "gi"  // g resembles global and i resembles index
// // check
// let regx1  = new RegExp(pattern,flag)

// // const check ="hello1 himansh2u"
// const check ="helilo abhhello himansh2u"
// const result =  regx1.test(check)
// // const result =  pattern.test(check)
// // // .test will not work if you have not converted both into regexp

// console.log(result)

// console.log(regx1)


/*+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++*/

//                            //  method 2

// let regx2 = /himanshu/gi  

// const check ="hello1 himansh2u"
// // const check ="hello874hi himanshu_89585649hj"
// // const check ="hel4lohello   67himanshu_89585649hj"



// const result1 =  regx2.test(check)
// //   //  //ye test method tabhi kaam karega jab regular expression ban chuka hoga aur result boolean value m hi dega
// console.log(result1)


/*++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ */

// let regx2 = /himanshu/gi

// const check ="hello himanshu how are u say hel6lo hi 1ii_himanshu again HIMANSHui90i means hello hi means hell9o"
// const otherresult = check.match(regx2)
// console.log(otherresult)

// const replaceresult = check.replace(regx2,'h-elo')
// console.log(replaceresult)


/*+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++*/

// //                    //   checking urls


const weburl ="https://anon30ymo3030us.30@gmail.com"
const urlresult =weburl.replace(/30/,"-")
console.log(urlresult)

const urlresult1 =weburl.replace(/\d\d\d\d/,"-")
console.log(urlresult1)

Spread and rest operator

The spread operator unpacks an iterable (like an array or string) into individual elements.

It's commonly used in:

1. Combining Arrays:

   
    const numbers1 = [1, 2, 3];
    const numbers2 = [4, 5, 6];
    const combinedNumbers = [...numbers1, ...numbers2]
   

2. Passing Arguments to Functions:

function sum(x, y, z) {
  return x + y + z;
}

const n = [11, 2, 3];
const result = sum(...n);
console.log(result)

3. Copying Arrays:

   
    const originalArray = [1, 2, 3];
    const copiedArray = [...originalArray];
   

   
   Rest operator: The rest parameter gathers remaining elements into an array within function parameters or array destructuring.

   It's used for:
   1. Variable-Length Function Arguments:

2. Array Destructuring:

    const [first, ...remaining] = [1,8 ,4,5,2, 3, 4];
    console.log(first)
    console.log(remaining)

Coding implementation:

// let a = [1, 2, 3,4]
// let b = [5,6,7,8]

// // let c = a.concat(b)
// // console.log(c)

// // let d = [ a , b]
// // console.log(d)

// //               //            //spread and rest operator
// // the below code is both spred and rest if depends on the use case
// const e = [...a , ...b]
//  // here this is spread
// console.log(e)


/**+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ */


// converting objects to array//

// TYPE 1: CONVERTING ARRAY TO ARGUMENTS//

// function hello(){

//     let a = Array.from(arguments)
//     let b = a.map(e=>e)
//     console.log(b)
// }
// hello(1,2,3)


//  TYPE 2: DIRECTLY CONVERTING INTO ARRAY

// function hii(...a)
// {
//     let b = a.map(e=>e)
//     console.log(b);
// }
// hii(2,3,6,4)

/*--------------------*/
// rest operator : when we have different values in arguments
// and we have to combine them then we can use rest operator


// spread operator : when we have to combine two array then we have
// to either use concat otherwise the output is array inside array
// so to overcome it and for seperation we have to use spread operator
/**/ 


// more exapmles of sperad operator

// const name = ["g" , 'gg']
// const name2 = ["h" , ...name,'hh']
// console.log(name2)


// const name3 = "hello howare you"
// console.log([...name3])
// console.log(...name3)


//   example of rest operator

// function testrest (...a){

//     return a
// }
// console.log(testrest(1,2,3))


/*
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++*/

// let set1= new Set()          // declaration of set
// console.log(set1.size)

// let array1 =[1,2,3,3,,4,5,3,2]
// // set allows only unique values

// // //TO CREATE A SET 
// const newset = new Set(array1)
// console.log(newset)
// console.log(newset.size)

// // //TO ADD A NEW NUMBER 
// newset.add(9)
// console.log(newset)

// // // TO CHECK WHETEHER THE LEMENET IS PRESENT OR NOT 
// console.log(newset.has(9))


// // //TO CLEAR THE ELEMENTS 
// newset.clear()
// console.log(newset)


// //set difference
function setdiff(set1,  set2)
{
    if (!(set1 instanceof Set) || !(set2 instanceof Set)) {
        throw new Error('Both setA and setB must be Sets+++++.');
    }
   return new Set ( [...set1].filter(element => !set2.has(element)))

}
// const set11 = new Set([1, 2, 3]);
// const set2 = new Set([2, 3, 4]);
// const diffSet = setdiff(set11, set2);
// console.log(diffSet)


// const set1 = new Set([1, 2, 3]);
// const array2 = [2, 3, 4]; 
// const diffSet = setdiff(set1, array2); 
// console.log(diffSet); 



// //MAP
let map = new Map()
console.log(map.size)



let array =[
    [1,"give"],
    [2,"krishna"],
    [3,"thor"],
    [4,"haryana"]
];

// let c =array.map((arrayelement)=>map.set(arrayelement[0],arrayelement[1]))
// console.log(c)

array.map((arrayelement) => map.set(arrayelement[0], arrayelement[1]));

console.log(map);

lt.38: link:https://hashnode.com/preview/662a992439252d00cfb66c8a